Locus of Symptom Limitation and Exercise Response to Bronchodilation in Chronic Obstructive Pulmonary Disease

Background: We previously reported that the occurrence of contractile fatigue of the quadriceps during exercise in patients with COPD reduced the likelihood of acute bronchodilation to improve the endurance time to constant work rate exercise. The purpose of the present study was to assess whether the perception of dyspnea and leg fatigue during exercise could be used to predict the exercise response to acute bronchodilation in this population. Methods: Sixty-eight patients with COPD performed either two constant work-rate cycling exercises or two endurance shuttle walking tests. These tests were preceded by nebulization of placebo or 500 mg ipratropium bromide. Changes in FEV1 and in the endurance time with bronchodilation were measured. The changes in quadriceps twitch force after exercise were evaluated. In addition, we assessed dyspnea and perception of leg fatigue on Borg scale as well as the locus of exercise limitation (dyspnea, leg fatigue, or both). Results: The locus of symptom limitation was useful to predict the exercise response to bronchodilation; patients stopping exercise because of leg fatigue or due to a combination of dyspnea/leg fatigue showed a smaller improvement in endurance time to constant work rate exercise with bronchodilation compared with those stopping because of dyspnea. Subjective and objective evidences of fatigue were related: patients who stopped exercising because of leg fatigue showed a larger fall in quadriceps twitch force compared to patients who stopped for dyspnea. Conclusion: The assessment of the locus of symptom limitation during constant work rate exercise is useful to predict the improvement in endurance time following acute bronchodilation in patients with COPD